Caveat Emptor
Some of the cheaper plywood verities have voids in their cores and occasional loose plies. They are intended for use in building construction as roof decks, shear wall skins, or for other structural purposes where such imperfections are acceptable. To use them for loudspeaker cabinets requires tapping with a hammer to find the bad sections to avoid. For front baffles, where the drivers are to be mounted, use several layers of cabinet grade plywood.
Regards,
WHG
Some of the cheaper plywood verities have voids in their cores and occasional loose plies. They are intended for use in building construction as roof decks, shear wall skins, or for other structural purposes where such imperfections are acceptable. To use them for loudspeaker cabinets requires tapping with a hammer to find the bad sections to avoid. For front baffles, where the drivers are to be mounted, use several layers of cabinet grade plywood.
Regards,
WHG
Generally speaking, the higher the density the better. I once measured some 15 ply BB and got around 0.7 g/cc. That's pretty high, but I'm sure there are others that are higher.
You certainly can go lower in density. However, more bracing and/or internal dampening will be required (i.e. higher aggravation factor).
You certainly can go lower in density. However, more bracing and/or internal dampening will be required (i.e. higher aggravation factor).
My experience is B and BB birch ply are fine and miles ahead of MDF, which always sounds dull and lifeless to me. The edge joints and even the adhesive type can be very influential in the end result. Taking the time to rout proper tongue and grooves for every panel and brace results in much higher overall enclosure stiffness. The baffle is always a weak point: often more hole than wood. I go for Tufnol for baffles if I can.
I'd love to try some bamboo ply. Anyone in the UK sourced some?
I'd love to try some bamboo ply. Anyone in the UK sourced some?
I could get a chunk of stranded bamboo and weight it. It is heavy, but then the reference is a set of 12mm BB Fonken vrs a set of 19.1mm Bamboo Fonken (we can only get the bamboo in the thicker material). The stranded is denser than the other bamboo we have used.
dave
Yes, your findings would be of interest. Please try and keep the density units consistent (g/cc). I have some MDF I'll weigh and share the info as well. I checked it once years ago out of curiosity and recall its density was a bit less than BB.
Thanks thornspawn. Google is a wonderful thing.
Here's a link to more wood densities expressed as Kg/CU. M.
Density of Wood
Looks like MDF isn't much different than BB.
Here's a link to more wood densities expressed as Kg/CU. M.
Density of Wood
Looks like MDF isn't much different than BB.
TUFNOL glass fabric grades 1.90-1.95.
Heavy and very tough. Can be joined with a high quality thermosetting resin.
Structurally a high grade plywood is hard to beat - I use a 13 ply 3/4" nominal (23/32") maple that comes prefinished with clear lacquer that is UV cured and finished to 1000 grit...it runs about $95 for a 4x8 sheet. It requires care in handling during fabrication to avoid scratches but the finish is better than I can obtain at home.
If your priority is stunning appearance then quality solid hardwood is my preference. Either kiln or air dried is acceptable as long as the moisture content is below 7%. Once you get it in your shop you want to give it at least 2 weeks to acclimatize to your prevailing humidity level before you start construction. The main caution in speaker building with solid wood (typically glued up to get the widths needed for larger speakers) is to allow for wood movement with changing seasonal humidity levels. The focus of this issue is in areas of construction where solid lumber crossgrain (which expands with increasing humidity) is attached to either solid lumber long grain or plywood (which does not "move" appreciably with humidity). There are a number of techniques to deal with this issue, the details depend on the particulars of your design.
One way to get the best of both worlds is to build the center portion of the speaker (top, bottom, front, back & internal bracing) out of plywood and the side panels from solid lumber. The solid side panels can hide the raw plywood edges and wood movement can be handled by screwing through the plywood from the inside using oversized holes and screws designed for attaching drawer fronts, which have large heads to cover the oversized holes. This approach requires that you add plywood "flanges" to the center section where it joins to the side panels.
Working around each material's strengths and weaknesses is more than half of the fun of the design process!
If your priority is stunning appearance then quality solid hardwood is my preference. Either kiln or air dried is acceptable as long as the moisture content is below 7%. Once you get it in your shop you want to give it at least 2 weeks to acclimatize to your prevailing humidity level before you start construction. The main caution in speaker building with solid wood (typically glued up to get the widths needed for larger speakers) is to allow for wood movement with changing seasonal humidity levels. The focus of this issue is in areas of construction where solid lumber crossgrain (which expands with increasing humidity) is attached to either solid lumber long grain or plywood (which does not "move" appreciably with humidity). There are a number of techniques to deal with this issue, the details depend on the particulars of your design.
One way to get the best of both worlds is to build the center portion of the speaker (top, bottom, front, back & internal bracing) out of plywood and the side panels from solid lumber. The solid side panels can hide the raw plywood edges and wood movement can be handled by screwing through the plywood from the inside using oversized holes and screws designed for attaching drawer fronts, which have large heads to cover the oversized holes. This approach requires that you add plywood "flanges" to the center section where it joins to the side panels.
Working around each material's strengths and weaknesses is more than half of the fun of the design process!
Attached is a table from some samples Chris dropped off.
It should be noted that from the point of view of getting panel resonances up, if you have 2 materials with the same stiffness, the lighter one is better.
Density will have some effect on damping & impedance (don't know which direction this goes), but the detail of the structure is likely more important.
I will follow with pictures,
dave
It should be noted that from the point of view of getting panel resonances up, if you have 2 materials with the same stiffness, the lighter one is better.
Density will have some effect on damping & impedance (don't know which direction this goes), but the detail of the structure is likely more important.
I will follow with pictures,
dave
Attachments
It seems your calculations are a bit off kilter. Your results are in units of CC/G. Take the inverse of your values and that will be G/CC and thus the result for BB becomes 0.716.. , close to what I measured. If you don't believe me, take a piece of BB and drop it in a bucket of water. If it floats, its density is < 1.0.
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Yes, Lignum Vitae (the most dense wood) has a density of 1.3 g/cm^2. Quite a bit more dense than BB ply.
A simplified formula for resonant frequency is
f=sqrt(k/m) were
k = spring constant (proportional to stiffness ) and
m=mass (which is proportional to density for a given thickness).
It gets a little more complex to calcualte on sheets of material in cabinet enclosures but the basic principle is the same.
MDF has a low k and high m when compared to many woods discussed here like oak, maple, cherry, ash etc. The BB will have a higher k but I am not sure what the density is in comparison to MDF.
P.S. If you want the highest resonant frequency use the lightest and most stiff material for a given thickness.
f=sqrt(k/m) were
k = spring constant (proportional to stiffness ) and
m=mass (which is proportional to density for a given thickness).
It gets a little more complex to calcualte on sheets of material in cabinet enclosures but the basic principle is the same.
MDF has a low k and high m when compared to many woods discussed here like oak, maple, cherry, ash etc. The BB will have a higher k but I am not sure what the density is in comparison to MDF.
P.S. If you want the highest resonant frequency use the lightest and most stiff material for a given thickness.
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If using solid wood, the question of kiln dried vs. air dried is at the hands of the kiln operator. IMHO.
If it is kiln dried incorrectly it will have ALOT of internal stresses that will cause the wood to warp during construction and over time. Even with good joinery, cracks will develop over time. Air dried typically has less stress (not zero) and will tend to be more stable. (usually it takes many months to properly air dry a hard wood and my patience isn't that high).
By stripping the wood and gluing into sheets, many of the stresses get released and what is left is distributed more evenly. As a result the piece is more stable over time.
If it is kiln dried incorrectly it will have ALOT of internal stresses that will cause the wood to warp during construction and over time. Even with good joinery, cracks will develop over time. Air dried typically has less stress (not zero) and will tend to be more stable. (usually it takes many months to properly air dry a hard wood and my patience isn't that high).
By stripping the wood and gluing into sheets, many of the stresses get released and what is left is distributed more evenly. As a result the piece is more stable over time.
Attachments
Absolutely correct that kiln-drying is frought with perils...try to go too fast & the wood can end up hard to work with & prone to defects. Air drying is by its nature gradual, but improper stacking & stickering can also wreck the wood. My preference is to go to a trusted source who will let you sort through tha pile (so long as you leave it tidy) for matching grain & figure. I like to get the wood roughsawn & planed one side to be able to see the figure & finish then dressing it to size at home.
You are right... don't even need to open the SS to verify, i can see the mistake in the formula in my head.... trying to squeeze that job in before going up to cook dinner.
I've just replaced the incorrect picture above.
Attached is the fixed spreadsheet if people want to add stuff to it.
We've built boxes with all but the dragon ply, IOE materials from best to worst are stranded bamboo, other bamboo, BB, and MDF trailing a long ways behind.
dave
Actually spruce has the best "weight to strength" ratio. Many light airplane parts were (are?) made from it.
Howard Huges' "Spruce Goose" comes to mind but that was really built mostly with birch and birch plywood.
Thanks P10 for the updated spreadsheet. I've added it to my speaker library.
...still have to get my MDF measurement done. I'm curious to see how close it comes to your 0.827.
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